Corrosion inhibition



United States Patent 3,220,866 CORROSION INHIBITION Arnold Joseph Rosenthal, Whippany, N.J., assignor to Celanese (Iorporation of America, New York, N.Y., a corporation of Delaware No Drawing. Filed May 25, 1962, Ser. No. 197,595 21 Claims. (Cl. 106181) lose to filamentary material and the like, these esters may be dissolved in halogen-containing organic solvents. By way of illustration, cellulose triacetate is dissolved in methylene chloride which may also contain minor amounts of co-solvents for the ester such as methanol, ethanol, isopropanol or the like, as well as small amounts of water. This solution or dope is then dry spun into filamentary cellulose triacetate, the solvent being evaporated by a current of warm air followed by recovery and purification prior to re-use. The spinning is effected by passage of the solution through one or more orifices in a metallic member generally referred to as a jet. It has been found that these jet-s, as well as other metal equipment contacted by the solvent during use and recovery, corrode rapidly and require frequent replacement.

It is accordingly an object of the present invention to minimize or prevent this corrosion of metallic members contacted by halogen-containing organic solvents for organic acid esters of cellulose.

Another object is to provide a solution of cellulose triacetate in methylene chloride, which solution can be dry spun without rapid corrosion of the spinning jet.

A further object of the invention is to provide a cellulose triacetate solution which is sufiiciently non-corrosive on metals to permit spinning through stainless steel jets.

Other objects of this invention will be apparent from the following detailed description and claims.

In accordance with one aspect of the present invention, to a halogen-containing organic solvent solution of the organic acid ester of cellulose there is added a stabilizer or mixture of stabilizers which inhibits corrosion of metallic members. The stabilizers must satisfy certain requirements in order to be suitable for use, viz., they must themselves be non-corrosive, they should not have any particular afiinity for the cellulose ester lest they contaminate articles produced therefrom, they should not deleteriously affect the physical properties of the cellulose esters, under conditions of use they should not endanger the operators, they should not irritate or sensitize the skin when worn and preferably they should be sufficiently inexpensive so that their cost will be compensated for by savings in the replacement cost of metal equipment or by improvements in the properties of the esters as a result of elimination of metallic contaminants.

The quest for suitable stabilizers is complicated by the fact that the exact mechanism of the corrosion is not fully understood. While it might be expected that the corrosion is the result of the presence of hydrohalic acids, stabilizers heretofore used to prevent corrosion in other systems or to bind any decomposition products of halogen-containing systems, e.g., organometal salts or acid binding agents such as triethylamine and triethanolamine, are ineffective in the instant situation. Moreover, the corrosion of the spinning jet-s is apparently independent of temperature, whereas if the corrosion were the result of decomposition with evolution of hydrogen halide it would be expected to be temperature-dependent.

It might also be theorized that the corrosion is due to oxidation but faces of jets exposed to air are even less corroded than those shielded from air. In addition, antioxidants such as hydroquinone ethers do not exert any appreciable inhibitory eifect on solutions of the character herein set forth.

It has now been found that if an organotin derivative of a carboxylic acid is incorporated into a solution of an organic acid ester of cellulose in a halogen-containing organic solvent, the corrosion of metal jets from such solution is markedly reduced or, indeed, virtually eliminated. The carboxylic acid from which the organotin derivative is formed may be either a mono carboxylc acid, e.g., acetic acid, butyric acid, caproic acid, la-uric acid, palmitic acid, oleic acid, be'henic acid, etc, or a dicarboxylic acid, e.g., maleic acid, fumaric acid, etc.

An example of a suitable organotin derivative of a mono carboxylic acid is a dibutyltin dilaurate. Suitable derivatives of dicarboxylic acids include alkyltin maleates wherein the alkyl group contains from about 2 to 10 carbon atoms. We have found that dibutyltin maleate is particularly suitable.

In addition, organotin derivatives of mixed maleic acid and a mono carboxylic acid are also suitable. Such mixed organotin derivatives are described in US. Patent 2,826,597, and may be illustrated by the following structural formula:

wherein R is an alkyl, aryl or aralkyl group, and R is an alkyl radical. Thus R may be any organic radical such as methyl, ethyl, propyl, butyl, lauryl, phenyl, benzyl, etc. Similarly, R may be derived from any monobasic aliphatic acid such as acetic, butyric, caproic, lauric, palmitic, oleic, behenic, etc.

We have found that the use of one of the foregoing organotin derivatives of a carboxylic acid is extremely effective in preventing corrosion of metal jets in a dynamic situation, i.e., under actual spinning conditions. This result is quite unexpected because when such an organotin derivative of a carboxylic acid is incorporated into a spinning solution and such solution is caused to contact a metal specimen under static conditions, i.e., wherein the metal specimen is simply placed into the spinning solution, no particular inhibition to corrosion is apparent. Thus, although the explanaton of the unexpected efficacy of the organotin derivatives of a carboxylic acid in preventing corrosion under dynamic situations and not under static situations is not presently understood, the fact remains that in actual spinning conditions the incorporation of such derivative markedly reduces corrosion.

The organotin derivative of a carboxylic acid will exert some beneficial action when present even in the most minute quantities. However, to obtain appreciable inhibition against corrosion, such stabilizer, when used alone, should be present in an amount at least 0.005 percent by weight of the solution. Generally, the range will be from about 0.005 to 0.5% of the solution, with a more preferred range being from about 0.01 to 0.1%. Even more than about 0.5% of stabilizer can be used, but since corrosion is substantially completely eliminated with lesser amounts, there is no need.

In accordance with another aspect of the invention, it has been found that if, along with such organotin stabilizer, a lower alkyl amine nitrite stabilizer and particularly a hydroxysubstituted lower alkyl amine nitrite such as 2- hydroxypropyl-amine nitrite is incorporated into the solution of organic acid ester of cellulose in halogen-containing solvent, a synergistic efiect takes place. That is, the amount of each stabilizer required to inhibit jet corrosion from such solution is markedly reduced to about 20 percent of the amount that would be required to obtain 4 chloride-methanol, such as are disclosed in abandoned US. application Serial No. 566,088, filed February 17, 1956, by Robert K. Davies and Arnold J. Rosenthal. The solutions there described comprise cellulose acetates havequivalent corrosion inhibition when using either the 5 ing an acetyl value in excess of 59.5% by weight expressed organotin stabilizer or the lower alkyl amine nitrite alone. as acetic acid (herein referred to as cellulose tria'cetate) US. Patent 2,927,031 teaches the incorporation of a lower dissolved in methylene chloride-methanol to a concentraalkyl amine nitrite into a halogen-containing organic sol tion of above 15% and preferably from 17 to 27%. The vent solution of an organic acid ester of cellulose and methylene chloride can range upwards from 80% of the further teaches that the amount of amine nitrite so incombined weights of methylene chloride and methanol corporatcd may be from about 0.005 to 0.5% by weight with about 90% or more p These Solutions of the solution. However, as heretofore pointed out, if generally contain small amounts of water, from about an organotin stabilizer, e.-g., dibutyl tin maleate, and a 0.3% of the weight of the solution up to the amount which lower alkyl amine nitrite stabilizer, e.g., IZ-hydroxywill create turbidity, although preferably water is present propylamine nitrite are both incorporated into such soluin no m re h n 6 y w g f the amount which ll tion, the amounts of each such stabilizer may be reduced create turbidity. The amount of Water which will create to about 20% of that required when either is used alone, turbidity will vary with the composition of the solution. i.e., from about 0.001 to 0.1% by weight of the solution. With the minimum concentration of 15% by weight of Thus, the use of the organotin stabilizer and lower alkyl cellulose triacetate in the solution and about 10% of amine nitrite together offers obvious economic advantages. 20 methanol in the solvent the turbidity point will correspond As has been previously pointed out, the present invento about 1.7% of water. tion finds particular application in dynamic situations, Following spinning, the amount of stabilizer adhered e.g., under actual spinning conditions. Thus, without the to the cellulose triacetate is extremely small and any small presence of either the organotin stabilizer or a stabilizing residual amounts will be removed during the wet treatmixture of the organotin stabilizer and lower alkyl amine ments to which fabrics made from said filamentary matenitrite stabilizer, the solution of organic acid ester of rials are normally subjected. cellulose in halogen-containing solvent will induce con- The following examples will further illustrate my insiderable corrosion of the metal jet as such solution is vention. Each jet was made of stainless steel, was linch spun therethrough. in diameter, and contained five holes, each 0.032 mm. in The solvent of the cellulose ester solution can be any diameter. In j g g j damage from eXtruSiOn, halogenated organic solvent but the preferred solvents are a numerical rating system was used to summarize the chlorine substituted lower alkanes such as methylene damage as revealed by microscopic examination. The chloride, ethylene dichloride, and the like. These may following system was employed: contain minor amounts of co-solvents or non-solvents for the esters, depending upon the properties desired for the of damage! Demfllits composition and the subsequent treatments to which it will Plts ill p y W311 1 be subjected. When a methylene chloride solution i to Ni k in h le n o r at j f 1 be used for dry spinning, for example, the methylene Rejected hole (fadlus enlarged 0-004II1111- at chloride solvent may contain as much as 20% by weight any Point 3 of volatile alcohols such as methanol, ethanol, propanol, 40 Maximum demeflts Permitted P hole, not isopropanol, and the like, the percentage being based on rejected 2 the combined Weights of methylene chloride and alcohol. Maximum demerits assigned P rejected 1116 3 Although water will decrease the solubility of the ester in the solvent, small amounts can be tolerated. The stabiliztotal demeritsX 100 ing action will be realized even in the presence of water. D amage Score per percent=m Organic acid esters of cellulose which can be used are preferably the lower alkanoic acid esters such as the acetate, propionate, butyrate, acetate-propionate, acetate- Examples y a e, and t e llke While the Invention 1s applicable Cellulose acetate having an acetyl value of 61.5% is to any esters which w1ll d1ssolve 1n the indicated solvents, dissolved in a mixture of 91 parts by weight of methylene excellent results are achieved when using cellulose acetate chloride and 9 parts by Weight of methanol to form a havlng all acetyl Content excess of about 595% and solution having a concentration of cellulose acetate of preferably 61.5% by weight calculated as acetic acid. 22% by i h based on the i h f Solvent Varying Such esters are substantially fully acetylated, i.e., free of amounts of dibutyl tin maleate or of Z-hydroxypropyl unreacted hydroxyl groups, and are hereinafter referred amine nitrite are incorporated into the solution, as shown to as cellulose triacetate although a small residue of unin Table I. The solution is spun at a temperature of reacted hydroxy groups may be present. 72 C. at a rate of 1200 meters per minute linear velocity The present invention is particularly useful in the dry of solution through the 0.032 mm. diameter hole type spinning of solutions of cellulose triacetate in methylene 316 stainless steel jets. The results are given in Table I.

TABLE I Stabilizer Damage Example Stabilizer Concen- Hours of Score,

tration, Extrusion Percent Percent A (control) 0. 00 72 0.01 30 0 1 Dibutyl tin maleate 8: g? 0. 01 500 67 0. 03 54 0 as as a 2a a 3 3 0105 500 0 The efiicacy of the dibutyl tin maleate stabilizer in preventing jet corrosion is obvious.

and about by weight of methanol, said solution containing water in an amount between a minimum of about TAB LE II Stabilizer Damage Example Stabilizer Concen- Hours of Score,

tration, Extrusion Percent Percent A (control) 0.00 72 100 Dibutyl tin maleate 0.01 48 0 4 h 169 0 ydroxypropyl amine nitrite- 0. 01 500 7 B 2-hydroxypropyl amine nitrite- 0. 005 42 67 0 do 0. 015 500 87 8' 232 a 01025 500 33 Example 4 0.2% by weight and a maximum of the amount which will The procedure described in Examples 1-3 was utilized, lg f j sz gg gg 5g 32 ggg ig g f g; zi zfi ggg gil 3} git gg gl g gzigzfi gg tigg gfig g suificient to substantially inhibit the corrosion of metals of iven in Table II and are com ared with the use of either an alkyl tin maleate wherein the alkyl groups contain 2 to g. p 10 carbon atoms as stabilizer, said maleate also being itlbutyl tm maleat? a1OPe.(EXamp1eS11 3) or the use 2- self non-corrosive to metals not having any particular gig g gz gig zg g tg fi gg gig 5 33382 8 6 affinity for said cellulose ester, and not deleteriously g g p affecting the physical properties of said cellulose triacetate. cent dlbmyl tm m.a1eate.1S.uSed along wlt.h 'Q P 5. A stable composition of matter non-corrosive to hydrqxypmpylamme the .corr 081.011 mhlbmon 1S metallic spinnerets contacted therewith in a spinning superior to that obtained using dlbutyl tin maleate alone process comprisino a Solution in a halogemcontaining D Exampla Wherem 003% dlbutyl tm maleate organic solvent of a lower alkanoic acid ester of cellulose showed a.damage Score i 9 i 500 q i 1S and a small amount suflicient to substantially inhibit the also Supenor to i corrpslon mhlbmon obtamed usmg corrosion of metals of an alkyl tin maleate wherein the hydroiiypmpylamme mtme alone Example alkyl groups contain 2 to 10 carbon atoms and of a hyz g ig g 23 3 g gf ggg ggfig mmte Showed droxy lower alkyl amine nitrite, said maleate and nitrite also bein themselves non-corrosive to metals not havin b The gi mnmg z q fi g any particular atfinity for said cellulose ester and no t e spun an e so vent recovere t ere om wit itt e or I I no corrosion of metal equipment contacted therewith, 5 3 1222222 3 afiectmg the physical propemes of sald cel- It is to be understood that the foregoing detailed de- 6 The c'omposifion of claim 5 wherein Said alkyl tin scription s given merely by way of IHHSFIBIIOH and tllat 4O maleate and said hydroxy lower alkyl amine nitrite are many vanallqns may e Ina-(1e therem Wlthout depa'mng each present in an amount equal to from about 0 001 to f tl-le SSH-1t P E l i' h I d 0.1% by weight of said solution. b g i f f my mventlon W eslre to secure 7.' A stable composition of matter, non-corrosive to yeersaen1s:

, metallic spinnerets contacted therewith in a spinning proc- Stable composmlm of i f non'corrpswe. on ess, comprising a solution of cellulose triacetate in a meta S contaciefl therewlih compnsmg a Solution m concentration of at least 15% by weight in a solvent comhalogen-containing organic solvent of a lower alkanoic prising methylene chloride and a lower alkanol the zfig g gg g fifiigig f g g ij g g i i g g gfi methylene chloride constituting at least about 80% by colroslvfi to metals not havmg any pllrtlcular afihllty for hibit the corrosion of metals of each of an alkyl tin Sald .cenulose not deletenously afiectmg the maleate wherein the alkyl groups contain 2 to 10 carbon p a 9 3 1 Egg: gz gg g s ig 3 533; Said or anotin atoms and a hydroxy lower alkylamine nitrite, said maleate cargox late is alk 1 tin maleate wherein the 31k on and nitrite being themselves non-corrosive to metals, not containig from aboutyz to 10 caflwn atoms and ai s 5 having any particular affinity for said cellulose triacetate, e 5 and not deleteriously afiecting the physical properties of said alkyl tin maleate is present in an amount equal to at Said cellulose triactate g g zi ggg ig g g ig fig to 8. A stable composition of matter, non-corrosive to p metallic spinnerets contacted therewith in a spinning procsplnperets conticted therewlth m ilspmmnlg Process ess corn rising a solution of cellulose triacetate in prising a solution of cellulose triacetate in a concentramthyleng chloride Said solution containing a small tion of at least 15% by weight in a solvent comprising methylene chloride and a lower alkanol, the methylene z ggig j gggg f gfigffififig i g gl glf g gzg 5 chlonde cqnstltutlpg at leas-t about 80% by Weight of the maleate said maleate and nitrite bein themselves nonsolvent, said solution containmg about 0 .0 05 to 0.5% by ormsiv t metals not havin an afticular amnit for weight and sufiicient to substantially inhibit the corrosion E t t d d 1 afl y th of metals of an alkyl tin maleate wherein the alkyl groups F 1 ose f I? 1 e e i V CC mg 6 contain 2 to 10 carbon atoms as stabilizer, said maleate also P Yslca Propertles O F 0S6 tlflacetat? being itself non-corrosive to metals, not having any par- A ProceSS for Stablhzmg a soluflon asamst corrqsfon ticular afiinity for said cellulose ester, and not deleteriously of metal contalfted fherewlth, Sald SOIUUOP P affecting the physical properties of said cellulose triacetate. a lower acld esfer of (361111105? dlssolved 111 a 4. A stable composition of matter, non-corrosive to l g nn lmng rg nl solvent, which process c mspinnerets contacted therewith in a spinning process, com- CP incorporating a Small amount Sufliclent to Substanprising a solution of cellulose triacetate in a concentratially inhibit the corrosion of metals of an organotin tion ranging from about 17 to 27% by weight in a solvent carboxylate in said solution, said carboxylate also being comprising about 90% by weight of methylene chloride itself non-corrosive to metals, not having any particular afiinity'for said cellulose ester, and not deleteriously alfecting the physical properties of said cellulose ester.

10. A process for stabilizing a solution against corrosion of metal contacted therewith, said solution comprising cellulose triacetate dissolved in methylene chloride, which process comprises incorporating a small amount sufficient to substantially inhibit the corrosion of metals of dibutyl tin maleate in said solution, said maleate also being itself non-corrosive to metals, not having any particular atfinity for said cellulose ester, and not deleteriously affecting the physical properties of said cellulose tn'acetate.

11. The process of claim 9 wherein said stabilizing proportion is from about 0.005 to 0.5% by weight of said solution.

12. In the production of filamentary material wherein a solution of a lower alkanoic acid ester of cellulose in a halogen-containing organic solvent is extruded through an orifice in a metallic member under conditions such that said cellulose ester is converted to filamentary material, the improvement which comprises incorporating in said solution a small amount of an organotin carboxylate, whereby corrosion of said metallic member and transfer .of metal to said solution and said filamentary material are inhibited, said carboxylate also being itself non-corrosive to metals, not having any particular aflinity for said cellulose ester, and not deleteriously affecting the physical properties of said cellulose ester.

13. The process of claim 12 wherein said stabilizing proportion is from about 0.005 to 0.5 by weight of said solution.

14. The process for stabilizing a solution against corrosion of metal contacted therewith, said solution comprising a lower alkanoic acid ester of cellulose dissolved in a halogen-containing organic solvent, which process comprises incorporating a small amount suflicient to substantially inhibit the corrosion of metals of a hydroxy lower alkyl amine nitrite and of an alkyl tin maleate wherein the alkyl groups contain 2 to carbon atoms, said maleate and nitrite also being themselves non-corrosive to metals, not having any particular afiinity for said cellulose ester, and not deleteriously affecting the physical properties of said cellulose ester.

15. The process of claim 14 wherein the hydroxy lower alkyl amine nitrite is 2-hydroxypropylamine nitrite and V wherein said alkyl tin maleate is dibutyl tin maleate.

'8 halogen-containing organic solvent is extruded through'an orifice in a metallic member under conditions such that said cellulose ester is converted to filamentary material, the improvement which comprises incorporating in said solution a small amount of a hydroxy lower alkyl amine nitrite and of an alkyl tin maleate wherein the alkyl groups contain 2 to 10 carbon atoms, whereby corrosion of said metallic member and transfer of metal to said solution and said filamentary material are inhibited, said maleate and nitrite also being themselves non-corrosive t-o metals, not having any particular aflinity for said cellulose ester, and not deleteriously afiecting the physical properties of said cellulose ester.

17. The process of claim 16 wherein the hydroxy lower alkyl amine nitrite is 2-hydroxypropylamine nitrite and wherein said alkyl tin maleate is dibutyl tin maleate.

18. The process ofclaim 16 wherein said stabilizing proportion for said hydroxy lower alkyl nitrite is from about 0.001 to 0.1% and wherein said stabilizing proportion for said alkyl tin maleate is from 0.01 to 0.1% by weight of said solution.

19. The composition of claim 1 wherein said organotin carboxylate is dibutyltin dilaurate.

20. The composition of claim 1 wherein said organotin carboxylate is a compound of the formula:

wherein R is selected from the group consisting of alkyl, aryl and aralkyl, and wherein R is alkyl.

21. The process of claim 12 wherein said ester of cellulose is cellulose triacetate and said halogen-containing organic solvent comprises methylene chloride.

References Cited by the Examiner UNITED STATES PATENTS 2,826,597, 3/1958 Gloskey 260429 2,857,413 10/ 1958 Weinberg 260-429 2,927,031 3/1960 Rosenthal 106-186 ALEXANDER H. BRODMERKEL, Primary Examiner.

MORRIS LIEBMAN, Examiner. 

4. A STABLE COMPOSITION OF MATTER, NON-CORROSIVE TO SPINNERETS CONTACTED THEREWITH IN A SPINNING PROCESS, COMPRISING A SOLUTION OF CELLULOSE TRIACETATE IN A CONCENTRATION RANGING FROM ABOUT 17 TO 27% BY WEIGHT IN A SOLVENT COMPRISING ABOUT 90% BY WEIGHT OF METHYLENE CHLORIDE AND ABOUT 10% BY WEIGHT OF METHANOL, SAID SOLUTION CONTAINING WATER IN AN AMOUNT BETWEEN A MINIMUM OF ABOUT 0.3% BY WEIGHT AND A MAXIMUM OF THE AMOUNT WHICH WILL BRING THE SOLUTION TO THE TURBIDITY POINT, SAID SOLUTION FURTHER CONTAINING ABOUT 0.005 TO 0.5% BY WEIGHT AND SUFFICIENT TO SUBSTANTIALLY INHIBIT THE CORROSION OF METALS OF AN ALKYL IN MALEATE WHEREIN THE ALKYL GROUPS CONTAIN 2 TO 10 CARBON ATOMS AS STABILIZER, SAID MALEATE ALSO BEING ITSELF NON-CORROSIVE TO METALS, NOT HAVING ANY PARTICULAR AFFINITY FOR SAID CELLULOSE ESTER, AND NOT DELETERIOUSLY AFFECTING THE PHYSICAL PROPERTIES OF SAID CELLULOSE TRIACETATE. 